I liked the 2 hour pilot as it was a hint of things to come. The clever wit/humour, unexpected turn (Jesse dying).......it was reasonably well put together for a newbie show runner like Joss at the time. Granted, Jesse didn't get a lot of follow up, but he was just trying get his show past the first season. My wife and I have been rewatching the series with my oldest daughter (she's 16) who's never seen the show before right now so the episodes are still pretty fresh for me, though we're all the way up to "Once More w/ Feeling" when watch our next episode.
General season 1 thought. I know vampires became punching bags and even punchlines in later seasons, but at least in Season 1, there was a real attempt to get the horror aspect of the show in there and I think Season 1 and to a lesser degree season 2 was generally scarier than the later season's portrayal of vamps. Sure, there's the occasional scary episode here in there like hush, but most gravitated more towards the action/humour than the horror feel Season 1 had.